The IEEE802.16 Working Group (WG) defines point-to-multipoint (P-MP) type communication schemes in which multiple wireless terminals (MSs: mobile stations) can connect to a wireless base station (BS). The IEEE802.16 WG (working group) defines two standards: the IEEE802.16d (802.16-2004) primarily for stationary communications and the IEEE802.16e (IEEE802.16e-2005) for mobile communications (see Non-Patent References 1 and 2 that will be described later) These standards define multiple physical layers, and techniques such as orthogonal frequency division multiplexing (e.g., the OFDM, OFDMA) are primarily used.
FIG. 19 illustrates a service image (example of the configuration of a wireless communication system) which is compliant to the IEEE802.16d/e. As depicted in FIG. 19, a system compliant to the IEEE802.16d/e is based on a point-to-multipoint (P-MP) type connection in which multiple MSs connect to one BS.
However, in such a service topology in which a BS and MSs connect each other in the P-MP manner, the service area is limited to the coverage area (cell) of the BS, resulting in a reduced communication rate at the cell edge.
For addressing this issue, the IEEE802.16 WG founded a task group (IEEE802.16j) for studying wireless relay stations (RSs) that relay communications between a BS and MSs, and the study is underway. FIG. 20 illustrates an example of the system configuration in which an RS is introduced. As depicted FIG. 20, the service area of the BS can be extended through the RS by carrying out communications with the MS that is located in the area outside the coverage of the BS through the RS.
On the other hand, in the technique disclosed in Patent Reference 1 described later, in a relay system using an RS, a BS determines scheduling for communications between the RS and an MS. The RS receives scheduling information on communication between the RS and the MS (information related to the configuration of wireless frames, allocation information on wireless resources (a DL/UL MAP in the OFDM scheme and the OFDMA scheme)) from the BS, and carries out communication control between the RS and the MS based on the scheduling information. In this configuration, it is possible to simplify configuration of the RS since scheduling processing is carried out by BS in the centralized manner.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-74325
Non-Patent Reference 1: IEEE Std 802.16™-2004
Non-Patent Reference 2: IEEE Std 802.16e™-2005
Non-Patent Reference 3: Eugene Visotsky, et al., “Proposal for Centralized HARQ Retransmission Scheduling”, IEEE C80216j-07—226, 2007 Mar. 5
However, in a situation in which an RS retransmits HARQ data to an MS on a DL, or in a situation in which the MS retransmits HARQ data to the RS on a UL, a transmission result regarding HARQ data between the RS and the MS is transmitted to a BS, and retransmission of HARQ data is invoked by generating scheduling information and transmitting it to the RS after the BS is notified with the results. As a result, there is a substantial lag between the time when the occurrence of the reception failure of the HARQ data and the time when the HARQ data is retransmitted. Thus, a significant delay is introduced into data transmission between the BS and the MS. Of course, such a delay is increased as the number of RSs relaying communications between the BS and the MS.
Note that the above-described Non-Patent Reference 3 describes pre-allocating a retransmission bandwidth such that an immediate retransmission is possible in a situation in which a BS is requested retransmission from an RS and an MS. However, no specific processing by the BS and the RS is not disclosed.